A new highly selective fluorescent turn-on chemosensor for cyanide anion

Ratiometric detection and monitoring of cyanide in biological, environmental and food samples by a novel triphenylamine-xhantane based fluorescent probe

BACKGROUND

As cyanide (CN-) is a significant hazard to the environment and human health, it is essential to monitor cyanide levels in water and food samples. Moreover, real-time visualization of CN-could provide an additional understanding of its critical physiological and toxicological roles in living cells. The fluorescence approach based on small organic probes is an effective way for the detection of CN-. In this approach, a triphenylamine-xhantane conjugate was applied to detect in many samples such as sewage water, soil, sprouted potato, apricot seed, and living cells.

RESULTS

We report a new ratiometric near-infrared fluorescent probe based on a triphenylamine-xhantane derivative for CN-sensing in many samples. The probe displays high selectivity for only CN- ions among a series of analytes. The addition of cyanide to the dicyanovinyl moiety of the probe disrupts π-conjugation followed by the interruption of internal charge transfer. Consequently, the emission peak of the probe shifts hypsochromically from 655 to 495 nm. There is a linear correlation between the emission intensity (I495) and cyanide level, with a detection limit of 0.036 μM. The probe has many advantages over many probes, such as NIR fluorescence, ratiometric response, low cytotoxicity (85.0 % cell viability up to 50.0 μM of the probe), good membrane permeability, fast response time (4.0 min), high selectivity, good photostability, and anti-interference capability.

SIGNIFICANCE

Although various probes have been reported in the literature, the use of triphenylamine-xhantane unit as CN- probe has yet to be explored. The probe can detect trace levels of cyanide in many samples such as sewage water, soil, sprouted potatoes, and apricot seeds. Furthermore, it is successfully utilized for the ratiometric fluorescent bioimaging of cyanide in living cells.

Spectroscopic and Theoretical Studies on the Selective Detection of Cyanide Ions by a Turn-On Fluorescent Chemo-Dosimeter and its Application in Living Cell Imaging

A new chemo-dosimeter AK4 containing quinoline fluorophore has rationally been designed, synthesised and characterized using 1H and 13C NMR and mass spectral techniques. The probe senses explicitly CN- ion through a dramatic enhancement in fluorescence over other commonly coexistent anions in H2O:DMSO (9:1 v/v) medium over a broad pH range (4-10). 1H NMR titration revealed the deprotonation followed by nucleophilic addition reaction of CN-, which was supported by 13C NMR and mass spectral examinations. The Job's continuous variation method indicated the formation of a 1:1 adduct between AK4 and CN- with a binding constant of 1.62 × 104 M-1. A limit of detection (LOD) towards CN- of 0.69 µM has been determined, which is much lower than the World Health Organization (WHO) recommended limit of CN- in drinking water (1.9 µM). The changes in the optical properties of AK4 upon reaction with CN- were delineated using Density Functional Theory (DFT) and Time-Dependent Density Functional Theory (TD-DFT) calculations. Moreover, fluorescence microscopic studies established that AK4 could be an effective probe for imaging intracellular CN- in HeLa cells.

A Turn-On Fluorescent Chemosensor for Cyanide Ion Detection in Real Water Samples

We have designed and synthesized a novel simple colorimetric fluorescent probe with aggregation-induced emission (AIE) properties. Probe 5-(4-(diphenylamine)phenyl) thiophen-2-formaldehyde W exhibited a turn-on fluorescent response to cyanide ion (CN−), which induces distinct visual color changes. Probe W exhibited a highly selective and sensitive ratiometric fluorescence response for the detection of CN− over a wide pH range (4–11) and in the presence of common interferents. The linear detection of CN− over the concentration range of 4.00–38.00 µM (R2 = 0.9916, RSD = 0.02) was monitored by UV-Vis absorption spectrometry (UV-Vis) with the limit of detection determined to be 0.48 µM. The linear detection of CN− over the concentration range of 8.00–38.00 µM was examined by fluorescence spectrophotometry (R2 = 0.99086, RSD = 0.031), and the detection limit was found to be 68.00 nM. The sensing mechanisms were confirmed by 1H NMR spectroscopic titrations, X-ray crystallographic analysis, and HRMS. Importantly, probe W was found to show rapid response, high selectivity, and sensitivity for cyanide anions in real water samples, over the range of 100.17∼100.86% in artificial lake water and 100.54∼101.64% in running water by UV-Vis absorption spectrometry, and over the range of 99.42∼100.71% in artificial lake water and 100.59∼101.17% in running water by fluorescence spectrophotometry. Importantly, this work provides a simple and effective approach which uses an economically cheap and uncomplicated synthetic route for the selective, sensitive, and quantitative detection of CN− ions in systems relevant to the environment and health.

Two cyanoethylene-based fluorescence probes for highly efficient cyanide detection and practical applications in drinking water and living cells

Cyanide detection methods are urgently needed due to the highly lethal to human beings. Herein, we report two fluorescence probes (Probe 1 and Probe 2) based on cyanoethylene group for cyanide anion (CN^-) detection. The selective recognition for CN^- was confirmed by the completely opposite green fluorescence of Probe 1 and red fluorescence of Probe 2 observed by fluorescence spectra and naked eyes. The probes take advantages of the large Stokes shift (~160 nm), rapid response (30 s), anti-interference performance and low detection limit (Probe 1: 12.4 nM, Probe 2: 101 nM). The sensing mechanism is certificated to the nucleophilic attack of CN^- to electron-deficient cyanoethylene group of probes, which was demonstrated by ¹H NMR titration, HR-MS, Job's plot and IR spectroscopy. Density functional theory (DFT) calculations were carried out to analyze the mechanism in theory. Further, practical applications were studied. Easy-to-use test strips treated with Probe 1 or Probe 2 are capable of CN^- detection in pure drinking water. The good biocompatibility and membrane penetrability have achieved the bioimaging capability of Probe 1 and Probe 2 in living HepG-2 cells, making the probes promising for use in real lives.

Turn-on fluorescent naphthalimide-benzothiazole probe for cyanide detection and its two-mode aggregation-induced emission behavior

Naphthalimide-benzothiazole conjugate (NBTZ) linked by cinnamonitrile was designed, synthesized, and fully characterized by NMR (¹H, ¹³C, DEPT, HSQC) and high-resolution mass spectrometry. NBTZ exhibited unique turn-on fluorescence in the presence of CN^- with relatively high selectivity compared to other anions such as SCN^-, HSO₄^-, ClO₄^-, NO₃^-, Cl^-, Br^-, I^-, and PO₄^-3 in tetrahydrofuran (THF). The detection limit for CN^- was found to be 3.35 × 10^-8 M in THF. The sensing mechanism was analyzed through ¹H, ¹³C, DEPT, and mass spectroscopy. NBTZ also showed two-mode aggregation-induced emission (AIE) in THF-H₂O mixtures. In a 30:70 THF-H₂O (v/v) mixture, the maximum AIE was observed at 430 nm (blue) because of the rotation of the CC bond between the naphthalimide ring and the phenyl ring was restricted. In 10:90 THF-H₂O (v/v), a new red-shifted AIE appeared at 490 nm (cyan), due to the extended π-conjugation induced by restriction of rotation of the CC bond between the benzothiazole and naphthalimide rings.

Tri-(2-picolyl)amine-modificated triarylborane: Synthesis, photophysical properties and distinguish for cyanide and fluoride anions in aqueous solution

We designed and synthesized a tri-(2-picolyl) amine (TPA) functionalized triarylborane, 1-(6-(4-(dimesitylboryl)phenyl)pyridin-2-yl)-N,N-bis(pyridin-2-ylmethyl)methanamine (PB2). The photophysical properties of PB2 were thoroughly explored. Moreover, PB2 can capture CN^- and F^- in aqueous solution through strong chelation induced by the synergy of a boron atom and metal ion gripped by TPA to display entirely different fluorogenic responses such as fluorescence enhancement for CN^- and fluorescence quenching for F^-. The results of TOF-MS-EI analysis and theoretical calculations indicate that the complexing of PB2 with CN^- formed a 2-to-2 adduct with a stabilized configuration, resulting in strong emission. The complexing of PB2 with F^- formed a 1-to-1 adduct with a loose configuration, resulting in weak emission. In pure water, the detection limit of PB2 for CN^- is 0.79 μM, and in H₂O/THF (1:9 v/v) system, the detection limits of PB2 for CN^- and F^- can reach 0.39 and 2.12 μM, respectively, indicating its potential application for effective detection and discrimination of CN^- and F^-.

Assessment of Chitosan Based Catalyst and their Mode of Action

Introduction:

The popularity of chitosan is increasing among the researchers due to its environment friendly nature, high activity and easy approachability. Chitosan based catalysts are not only the most active and selective in catalytic reaction, but their “green” accessibility also makes them promising in organic catalysis. Chitosan is commonly extracted from chitin by alkaline deacetylation and it is the second abundant biopolymer in nature after cellulose. Chitosan based catalysts are advantageous by means of non-metallic activation as it involves small organic molecules. The robustness, nontoxicity, the lack of metal leaching possibility, inertness towards moisture and oxygen, easy handling and storage are the main advantages of organocatalysts. Traditional drawbacks associated with the metal-based heterogeneous catalysts, like longer reaction times during any synthesis, metal-leaching after every reaction and structural instability of the catalyst for prolonged recycling experiments are also very negligible for chitosan based catalysts. Besides, these catalysts can contribute more in catalysis due to their reusability and these special features increase their demand as the functionalized and profitable catalysts.

Objective:

The thorough description about the preparation of organocatalysts from chitosan and their uniqueness and novel activities in various famous reactions includes as the main aim of this review. Reusable and recycle nature of chitosan based organocatalysts gain the advantages over traditional and conventional catalyst which is further discussed over here.

Methods and Discussions:

In this article only those reactions are discussed where chitosan has been used both as support in heterogeneous catalysts or used as a catalyst itself without any co-catalyst for some reactions. Owing to its high biodegradability, nontoxicity, and antimicrobial properties, chitosan is widely-used as a green and sustainable polymeric catalyst in vast number of the reactions. Most of the preparations of catalyst have been achieved by exploring the complexation properties of chitosan with metal ions in heterogeneous molecular catalysis. Organocatalysis with chitosan is primarily discussed for carbon-carbon bond-forming reactions, carbon dioxide fixation through cyclo- addition reaction, condensation reaction and fine chemical synthesis reactions. Furthermore, its application as an enantioselective catalyst is also considered here for the chiral, helical organization of the chitosan skeleton. Moreover, another advantage of this polymeric catalyst is its easy recovery and reusability for several times under solvent-free conditions which is also explored in the current article.

Conclusion:

Important organocatalyzed reactions with either native chitosan or functionalized chitosan as catalysts have attracted great attention in the recent past. Also, chitosan has been widely used as a very promising support for the immobilization of catalytic metals for many reactions. In this review, various reactions have been discussed which show the potentiality of chitosan as catalyst or catalyst support.

A new colorimetric and ratiometric fluorescent probe for selective recognition of cyanide in aqueous media

A simple naphthopyran derivative (L) has been synthesized as a colorimetric and ratiometric fluorescent probe for cyanide sensing in the aqueous DMSO medium and paper strips. The nucleophilic addition of CN^- to this probe blocks the π-conjugation and the intramolecular charge transfer (ICT) transition between naphthopyran and benzoindolium moieties and consequently results in remarkable color and spectral changes. Upon addition of cyanide, L displayed a ratiometric fluorescence response with a blue shift of the peak position and a noticeable color change from fuchsia to colorless within 90s. The probe exhibits high selectivity and sensitivity toward CN^- over other anions and the detection limit was calculated to be 7.56×10^-7M, which is well below the WHO cyanide standard in drinking water (1.9μM). In addition, the excitation and emission of the probe were within the visible wavelength range, which could benefit an application of the probe in an inexpensive portable cyanide sensor. The sensing ability of L has been successfully applied in real water samples. Furthermore, test strips based on L were fabricated, which can act as convenient and efficient test kits for detecting CN^-.

Strategies Towards the Synthesis of N2-Substituted 1,2,3-Triazoles

The chemistry of 1,2,3-triazoles gained much attention since the discovery of the copper catalyzed Alkyne-azide cycloaddition (CuAAC) reaction which delivers exclusively the 1,4-regioisomer in high yields. On the other hand there is still no universal methodology capable of delivering the N2 substituted regioisomer. The unique properties of these N2-substituted 1,2,3-triazoles have stimulated synthetic efforts on the developments of methodologies capable of delivering it in high yield and selectivity. These efforts are the subject of the presented review.

A new disulfide Schiff base as a versatile “OFF–ON–OFF” fluorescent–colorimetric chemosensor for sequential detection of CN− and Fe3+ ions: combined experimental and theoretical studies

A new disulfide Schiff base as a versatile “OFF–ON–OFF” fluorescent–colorimetric chemosensor has been synthesized for sequential detection of CN⁻ and Fe³⁺ ions.

Substituted 2-Aminobenzothiazoles Salicylidenes Synthesis and Characterization as Cyanide Sensors in Aqueous Medium

(E)-2-((benzo[d]thiazol-2-ylimino)methyl)-4-nitrophenol 1 and (E)-2-(((6-methoxybenzo[d]thiazol-2-yl)imino)methyl)-4-nitrophenol 2 were synthesized efficiently under microwave conditions. The structures were confirmed using IR, ¹H NMR, and 13C NMR. UV-vis. Fluorescence investigations demonstrated that 1 and 2 are sensitive and selective sensors for detection of cyanide over all other anions SCN−, AcO−, N₃−, H₂PO₄−, H₂AsO₄−, F−, Cl−, Br−, and I− in aqueous media. Cyanide induces colorimetric change from pale yellow to dark yellow and from transparent to pale yellow for 1 and 2, respectively. It enhances the absorption at wavelengths 385 nm and 425 nm of 1 and 385 nm and 435 nm of 2. Acidic anions H₂PO₄− and H₂AsO₄− displayed significant interference with the interaction of cyanide and sensors 1 and 2. Sensor 1 has lower detection limit (LDL) 1 × 10−6 M, while 2 has LDL 1.35 × 10−6 M.

A new fluorescent and colorimetric chemosensor for Al3+ and F−/CN− based on a julolidine unit and its bioimaging in living cells

A novel multifunctional chemosensor HL bearing a julolidine unit and a Schiff base unit has been synthesized. As a fluorescent sensor, HL exhibited excellent selectivity and high sensitivity to Al³⁺ and F⁻/CN⁻ with a low detection limit in acetonitrile. Moreover, HL also showed good colorimetric selectivity to F⁻/CN⁻; a solution color change from colorless to light yellow in acetonitrile was observed by the ‘naked-eye’. The properties of HL with Al³⁺ and F⁻/CN⁻ were studied by UV-vis absorption spectroscopy, fluorescence spectroscopy, high-resolution mass spectrometry and ¹H NMR titration. Furthermore, the cell imaging experimental results indicated that the chemosensor HL could be applied for the detection of Al³⁺ in living cells.

A novel multifunctional chemosensor HL bearing a julolidine unit and a Schiff base unit has been synthesized.

Multi-ion detection and molecular switching behaviour of reversible dual fluorescent sensor

The selective chemosensing behaviour of imidazole bisthiocarbohydrazone (IBTC) towards F^- and Cu²⁺ are studied via colorimetric, UV-Visible, fluorescence spectra studies, and binding constants were calculated. The ¹H NMR titration study strongly support that the deprotonation of IBTC followed by the hydrogen bond formation via N1H1 and N2H2 protons with fluoride ion. The fluorescence inactive IBTC-Cu complex became fluorescence active in the presence of perchlorate (ClO₄^-) ion. The selective detection of perchlorate ion was also explained. The F^- sensing mechanism of IBTC has been investigated by Density Functional Theory (DFT) and Time-Dependent Density Functional Theory (TDDFT) methods. The theoretical outcomes well reproduce the experimental results. And it concluded the NH protons, nearby the imine group was first captured by the added F^- ion and then deprotonation happened followed by the formation of hydrogen bond. The IBTC found good reversibility character with the alternative addition of Ca²⁺ and F^-. The multi-ion detection of IBTC was used to construct the NOR, OR and INHIBITION molecular logic gates.

Several hemicyanine dyes as fluorescence chemosensors for cyanide anions

Four hemicyanine dyes as chemosensors for cyanide anions were synthesized easily. Their photophysical properties and recognition properties for cyanide anions were investigated. The results indicate that all the dyes can recognize cyanide anions with obvious color, absorption and fluorescence change. The recognition mechanism analysis basing on in situ (1)H NMR and Job plot data indicates that to the compounds with hydroxyl group, the recognition mechanism is intramolecular hydrogen bonding interaction. However, to the compounds without hydroxyl group, cyanide anion is bonded to carbon-carbon double bond in conjugated bridge and induces N(+)CH3 to neutral NCH3. Fluorescence of the compounds is almost quenched upon the addition of cyanide anions.

Structure–reactivity correlation in selective colorimetric detection of cyanide in solid, organic and aqueous phases using quinone based chemodosimeters

The five new colorimetric chemodosimeters sense cyanide selectively and sensitively in aqueous and organic media via a nucleophilic addition mechanism exhibiting quantitative structure–reactivity correlation.

An aggregation-induced emission enhancement fluorescent benzoxazine-derived macromolecule: catalyst-free synthesis and its preliminary application for the determination of aqueous picric acid

An aggregation-induced emission enhancement macromolecular benzoxazine derivative was synthesized by a catalyst-free Mannich reaction and showed a fluorescence quenching response towards nitro compounds.

A colorimetric and ratiometric fluorescent probe for the selective detection of cyanide anions in aqueous media and living cells

Based on the internal charge transfer (ICT) mechanism, a novel colorimetric and ratiometric fluorescent probe was developed for highly selective and sensitive detection of cyanide ion in aqueous media.

A highly selective and sensitive acylhydrazone-based turn-on optical sensor for Al3+

The fluorescence turn-on probing of Al³⁺ in ethanol was realized by the utilization of a type of conjugated acylhydrazone-based compound.

A simple Michael acceptor type quinoline derivative for highly selective sequential recognition of CN− and Cu2+ in aqueous solution

A 2-(quinolin-2-ylmethylene) malononitrile (6) chemosensor capable of sensing cyanide and copper ions was designed through a sequential reaction with the two toxins. Significant color changes could be distinguished by the naked eye on UV lamp.

A highly selective SBA-15 supported fluorescent “turn-on” sensor for the fluoride anion

TSBA (or ASBA) remained stable upon prolonged exposure to UV light (losing ∼0.12% of its fluorescence intensity), and was highly selective towards F⁻ over other common anions (Cl⁻, Br⁻, I⁻, HPO₄²⁻, ACO⁻, and NO₃⁻).

A new coumarin based chromo-fluorogenic probe for selective recognition of cyanide ions in an aqueous medium

The optical behavior of a simple intramolecular charge transfer (ICT) fluorescent probe, a coumarin-nitrobenzene conjugate (CNB), has been described to detect cyanide (CN⁻) selectively in buffered aqueous media.